Transmission and control mechanism



Jan. 11, 1944.

F. A. PARSONS TRANSMISSION AND CONTROL MECHANISM Original Filed A1 Jri11'7, 1940 5 Sheets-Sheet 1 OINVENTUR: M4?

F. A. PARSONS TRANSMISSION AND CONTROL. MECHANISM Original Filed April17, 1940 5 Sheets-Sheet 2 Jan. 11,1944.

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TRANSMISSION AND CONTROL MECHANISM Original Filed April 17, 1940 5Sheets-Sheet 3 I as 36 A I N VEN TUE:

Jan. 11, 1944. F. A. PARSONS 2,339,102

TRANSMISSION AND CONTROL MECHANISM I Original Filed April 17, 1940 5Sheets-Sheet 4 ///////////////A WM Ill-11100111047 ma Fitz-LEE. $046MPatented Jan. 11, 194.4

TRANSMISSION AND CONTROL MECHANISM Fred A. Parsons, Milwaukee, Wis.,assignor to Kearney & Trecker Corporation, West Allis, Wis., acorporation of Wisconsin Original application April 17,1940, Serial No.

330,051. Divided and this application November 10, 1941, Serial N0.418,468

10 Claims.

This invention relates generally to transmission and control mechanism,and more particularly to apparatus for eliminating lost motion andattendant backlash or overrun in machine tool driving trains.

This application is a division of my copending application Serial No.330,051, filed April 1'7, 1940.

A purpose of the present invention is to provide a transmissionmechanism in combination with improved means responsive to variations inthe torque being transmitted, and operative in a manner such that thetorque variations may be utilized for control or elimination of backlashor overrun in certain portions of the transmission train, and especiallyto prevent overrun in the trainsuch as may occur, for example, in amilling machine table drive where the cutting pressure urges the tableahead of its driving train.

A further purpose is to provide an improved torque responsive device incombination With a reversible table transmission, the torque responsivedevice being arranged for operation at least in part in accordance withthe direction of movement of the table transmission.

A further purpose is to provide an improved torque responsive device incombination with a table transmission and a reversible spindle transmission, the torque responsive device being arranged for operation atleast in part in accordance with the direction of rotation of thespindle 5 transmission.

A further purpose is to provide an improved torque responsive device incombination with a reversible table transmission and a reversiblespindle transmission, the torque responsive device being arranged foroperation in part in accordance with the direction of table movement andin part in accordance with the direction of rotation of the spindle.

A further purpose is to provide an improved torque responsive device incombination with a reversible table transmission including meansshiftable for alternative feed and quick traverse ratesof tablemovement, the torque responsive device being arranged for operation in.part in accordance with the direction of table movement and in part inaccordance with the rate of table movement.

A further purpose is to provide an improved torque responsive devicecombination with a reversible table transmission having two rates ofmovement in both directions and a reversible spindle transmission, thetorque responsive device being arranged for operation in part inaccordance with the direction and rate of table movement and in part inaccordance with the direction of spindle rotation.

A further purpose is to provide animproved brakemeans in combinationwith a torque responsive device and a table transmission, the brakemeans being arranged in a manner to be regulated in accordance with theposition of. the torque responsive device.

A further purpose is generally to simplify and improve the constructionand operation of machine tools, and particularly of milling machines,and especially for the purpose previously mentioned; and still otherpurposes will be apparent from the specification.

The invention consists of the construction and combinationof parts asherein illustrated, described and claimed, and in such modifications of.the structureillustrated and described as may be equivalent of thesubjoined claims.

Throughout this specification the same reference characters have beenused to indicate the same parts, and in the drawings:

Figure l is a right side elevation of a milling machine in which .theinvention is incorporated in certain of its aspects.

Figure 2 is a front elevation of. the same machine.

Figure 3 is a partial section taken approximate- 1y along the line 33 ofFig. 1 and enlarged.

Figure 4 is a sectional development of transmission and other mechanism,taken approximatelyalcng line -44 of Fig. 3.

Figure 5 is a section of transmission and controlmechanism takenapproximately along line 5-5 of Fig. 2, and enlarged.

Figure 6 is an enlarged sectional view of a rate change deviceshown inFig. 4.

Figure 7 is a diagram showing the construction and operatingrelationship of certain torque responsive mechanism and backlasheliminating means, as incorporated in'themachine-of Fig. 1.

Figure 8 is a diagram showing -the operating relationship of the torqueresponsive mechanism and-backlash eliminating device of Fig. 7 withcertain modifications and additions.

Figures 8A, 8B are force charts showingcharacteristics during certainmodes of operation of the machine.

Figure. 9 is a, diagram illustrating possible direction relationship ofthespindle and table of the machine.

Figure .10 is a section of certain valves shown in Fig. 8.

Figure 11 is a. diagram showing theoperating I relationship of thetorque responsive mechanism and backlash eliminating device of Fig. 7with other modifications and additions, and

Figures 11A, 11B are force charts indicating characteristics duringother modes of operation of the machine.

The machine illustrated in Fig. l is a milling machine which includes acolumn 26, a tool spindle 2! rotatably supported on the column, and awork support or table 22 guided for movement o a saddle 23 in adirection transverse to the axis or the spindle, the saddle beingsupported for cross movement on a knee 24 which is vertically movable onthe column. The knee, saddle and table together provide for tablemovement relative to spindle 2| in three mutually transverse paths.

The spindle 2|, Fig. 1, is driven from a power source such as a motor25, through a main clutch generally denoted by the numeral 26. Thespindle transmission may be of any suitable typ but in the presentmachine includes rate change and reversing mechanism of the formdisclosed in my copending application Serial No. 126,779, filed February20, 1937, which matured into Patent No. 2,203,743, dated June 11, 1940,and will not, therefore, here be described in detail. Clutch 26 may beengaged by one direction of movement of a hand lever I85, Fig. 1. Theother direction of movement of the clutch hub engages a brake, generallydenoted by the numeral 29. A gear 33 i driven when the motor 25 isrunning, and forms the initial drive gear of a table quick traversedrive train later described. A gear 3| i driven only when clutch 26 isengaged, and forms the initial drive gear for a table feed rate trainlater described.

The feed and quick traverse trains just mentioned are alternativelyconnectible to drive a rotatable sleeve 32, Figs. 3, 4, carried in a boxor housing 23a, fixed on saddle 23. The quick traverse train includesthe initial gear 30, an idler gear train 30, Fig. 1, a gear 33, a shaft34, an extensible universal joint haft device 35, a shaft 36, Figs. 1,4, a sleeve 31 rotatably journaled in the housing 23a and slidablysplined with shaft 36, a jaw clutch 39 which includes a shiftable member39a, and gears 43, 4|, which drive the sleeve 32 from clutch 39 but onlywhen the clutch 39 is engaged.

The feed train includes the initial gear 3|, an idler gear train 42,Fig. 1, a gear 43, a shaft 44, an extensible universal joint shaftdevice 45, a shaft 45, Figs. 1. 4, a sleeve 41, Figs. 3, 4, rotatablyjournaled in the housing 23a, and slidably splined with shaft 46, astepless feed rate changer generally denoted by the numeral 48, a torquemeasuring device generally denoted by the numeral 4-9, gears 59, and anoverrunning clutch device generally denoted by the numeral 52, adaptedto drive the sleeve 32 at a feed rate that is variable according to theadjustment of rate changer 53, but which drives only when the clutch 35of the quick traverse train is disengaged.

The overrunning clutch 52, Fig. i, may be of any suitable type, but inthis instance is of a well-known form which includes an inner member 52afixed on the sleeve 32, an outer member 5211 fixed on or integrallyformed with the gear 5 I, and clutch rollers such as 520, the innermember having cam surfaces whereby springs, not shown, may operateagainst therollers to wedge the rollers for the outer member to drivethe inner member except when the inner member is driven at a faster ratethan the outer member and in the same direction, as occurs when theclutch 39 of the quick traverse train is engaged. By this arrangementthe sleeve 32 is alternatively driven at quick traverse rate or at feedrate accordingly a the clutch 39 is engaged or disengaged, the directionof rotation being the same in either case.

The table 22 may be driven in either direction from the sleeve 32through a table reverser gen erally denoted by the numeral 54, Fig. l,which includes friction clutches 54a, 5% each comprising a set of clutchplates in which the alternate plates are keyed with sleeve 32 and withthe extended and enlarged hubs of associated bevel gears 51, 58, wherebyan intermediate bevel gear 53 may be driven in opposite directionsaccordingly as clutch spools 56c, 54d are unitarily axially shifted inthe one or the other direction, the clutch spools having an intermediateposition in which neither clutch is engaged. Bevel gear 59 is connectedto drive a table screw 63, Fig. 3, through a shaft ti and a bevel gearpair 62, 53, the screw 60 being lidably splined in the bore of gear 53and engaging a nut 54 fixed in saddle 23. The screw it is squared at 65afor application of a crank, not shown, for manual adjustment of thetable in either direction.

Either the saddle 23 or knee 24 may be driven in either direction fromsleeve 32, Fig. 4, through a shaft 65, Figs. 4, 5, gears 51, 68, asuitable reverser, a shaft ill, a gear II fixed on shaft 'Hl, gears 2,13 respectively associated with a suitable knee selector clutch and asaddle'selector clutch 15, the selector clutches providing shiftableelements E la, 15a, Fig. 5, sutably interlocked in such manner thatengagement of the one clutch disengages the other. The saddle and kneetransmission and control mechanism is more fully described in saidcopending application and need not here be further described.

The quick traverse selector clutch 39 is under the operative control ofthe vertical movements of a hand lever I57, Figs. 1, 2, which is mountedfor universal pivotal movement, and the table reverser 54 is similarlyunder the control of the horizontal movements of the same hand lever.The control connections may be effected in a variety of ways, apreferred method being fully described in said copending applicationand, since the particular method does not concern this application, itneed not here be further described.

The feed rate changer unit 43, Figs. 4 and 6, is similar to the ratechanger disclosed in a copending application Serial No. 52,095, filedNovember 1935, and will therefore here be only briefly described. Therate changer includes a driving gear 9! fixed on the sleeve 41, a drivengear 32 fixed on another sleeve 93 which is rotatably mounted on sleeve#31, and gears such as fixed on shafts 35, preferably three,equiangularly spaced and each simultaneously engaging the driving gearQl and driven gear 92. The shafts 95 are each journaled in a cagegenerally denoted by the numeral 95, which is supported for independentrotation coaxial with sleeve 47, the cage including a sleeve portion 95aand flange portions 9% and 96c fixed with sleeve 35a and respectivelycarrying the bearings for the opposite ends of shafts at, the hearingsin this instance being anti-friction bearings such 91, 98.

Fixed for rotation or integral with each of shafts 95, Fig. 6, areccnically tapered friction rolls such as 99, the axis of the shafts 35being angularly disposed with respect to the axis of drive sleeve 41, atsuch angle that the outer pe- 49b, Figs: ,;7, 8:;and; 11, respectiveyzfixed. with. the drivensleeve 93of-;the*rate changer Fluid is.

riphery of each of the conical rolls standsyparallel with theaxis of thedrive sleeve. Frictionally simultaneously engaging the peripheries of,each of the rolls 99 there .is a non-rotatable friction ring I carriedby a frame generally denoted by the numeral ml, the frame together withthe ring I00 being adjustable in a path parallel with the axis of thedrive sleeve 47, whereby to engage ring I00 with the outer periphery ofrolls 99at various points of different roll diameter, the frame beingslidably guided for such movement on spaced guide rods I02, I03, Fig. 3,to be shifted by means later described. Ring I00 is prevented fromrotation and is carried by frame Hll in a manner permitting of a certainamount of adjustment relative to the frame whereby to simultaneouslyengage the periphery of each of the friction rolls 99 with equalpressure and at corresponding roll diameters, but since the details ofthe ring mounting do not concern the present invention they will nothere be described.

The friction contact between the rolls 99, Fig. 6, and ring I00 forceseach roll and its companion gear 94 to revolve whenever cage 96 isrevolved, and at a gear speed determined in part by the diameter ofrolls 90 at the point of ring contact. As the ring I0!) is axiallyshifted it contacts rolls 90 at points of differing roll diameter andchanges the relative speed of the gears. Thus as the ring is adjusted toengage the smaller diameter of the rolls 90 the speed of the rolls andof the gears 94 increases, and vice versa, and the relationship of thevarious parts of the rate change device 08 is such that when sleeve i?is driven at a constant speed the adjustment of ring I 00 will enforce avariable speed on driven gear 92. With the parts proportioned as shownin Fig. 6 the speed of driven gear 02 may be any of a stepless series ofspeeds having a range from zero speed, obtained When ring 100 isengaging a small diameter of rolls 99, to a maximum speed which issomewhat less than the speed of drive shaft 45, depending on the ratioof the driving and driven gears Si, 02, the ratio of the smallest andlargest diameters of rolls 90, etc.

For the adjustment of the output speed of the rate changer 48 the ringI00 is axially shifted by mechanism as follows: A shifter fork I20,Figs. 3, 4, and 6 engages the frame I0! and is uided on a rotatable camshaft I2? and a rod I28. Shaft I21 is provided with a cam groove 522 awhich is engaged by a pivoted follower member I29 carried by the forkI28, thecam shaft being rotatable from a hand wheel I30 fixed on a shaftI3! and connected with the cam shaft by bevel gears I32, 533. Agraduated feed dial I30 is rotatably carried on shaft I 3I and readableagainst an indicator I35, the dial preferably. being graduated forsomewhat less than one revolution thereof to correspond with the rangeof speeds available from therate changer 08, which ordinarily requiresseveral revolutions of cam shaft I27 to effect. Reduction gearing istherefore provided between shaft I3! and dial E34, including a pinionI3la, an internal gear I3 la, and an idler I35. The cam groove I2'la maybe of varying angle, as shown, whereby to effect a preferred spacing ofthe graduations of dial I34 such, for example, as to provide numberedgraduations at equal spacing on the dial but corresponding to the termsof a geometrical progression- The torque measuring device 48 includesrelatively rotatable piston and cylinder members 48 and wtih the feedtrain; gear. 50. supplied to the cylinder 4%, Fig. '7, from apositiveacting pump I05, of any suitable form, driven from the continuouslyrunning quicktraverse train sleeve 37, as by gears I06, I01, the'fluidbeing carried from the output port I05a-of the pump through closedchannel means, as by a channel I08, a stationary coupling member I09,

Fig. 4:, a rotary coupling member I I0, an annular groove Illla, anddrilled channels III, H2, in a manner to continuously urge relativerotation of piston and cylinder members 49a, 49b in the directionopposite to that urged by the transmission load carried by the gear 50.Except as it finds outlet through. an overload relief valve 498, Fig.'7, fluid from pump I05 can escape only after the fluid pressure onpiston member 490. has rotated the piston member against the resistanceof the transmission load sufficiently for exposure of a drain channelII3, the fluid pressure in channel I08 therefore normally beingproportional to the torque load on gear 50. To provide a predeterminedminimum fluid pressure in the channel I08, the piston member 49a of thetorque measuring device 49 is continuously urged, in a direction tocover the outlet port H3, by the means of a plunger 490, the desiredminimum fluid pressure being determined by the pressure of a plungerspring 49d, which is adjustable by the means of a spring abutment screw402. In addition to other uses, later explained, the device 49 operatesas a hydraulic cushioning and shock absorbing device in the mechanicaltable train.

During the feed rate operation of table 22, and particularly duringoperations generally known as climb cutting, it is very desirable thatthere should be no lost motion between the table screw 00 and nut 64such as-might result in chatter or vibration or permit the cutter tosuddenly pull itself into the work at a rate faster than the selectedfeed rate. To eliminate such lost motion and automatically establish aforce opposing axial lost motion between the screw and nut 64 there isprovided the following structure: Screw 60, Figs. 3, '7, is constructedwith threads having side faces at such angle that axial pressure hasrelatively little tendency to initiate or resist lateral movement of thescrew. A portion of the nut is cut away at one side of the nut axis, asat 64b, Fig. 3, and in the space thus provided there is a member 200which may be acted upon by a piston device generally denoted by thenumeral 20I including a piston 202 operated by fluid pressure suppliedthrough channels 203, 204, 205, Figs. 3, 7, from the channel I00,whereby the piston pressure varies in accordance with the feed torqueload on the torque device 49 of the feed train except that a minimumvalue is established by the spring 49d, and-a maximum value by anoverload device I98. The operation of pistondevice 20I is to force thescrew laterally to a pres,-v

sure contact acting between both sides of each screw thread and thecorresponding both sides of the nut threads, there being clearance atthe top and bottom of the threads to permit such engagement, even afterwear takes place. Where the screw and nut are properly fitted there isvery little lateral movement required and theresult is to eliminate allbacklash orlost motion between the screw and the nut. Moreover, thepressure connection is'xsuch that during table movements atquick'traverse rate, and during manual table movement from the squaredscrew end 60a, there is a minimum of lateral pressure, the pressure thenbeing reduced to that established by the spring 49d.

The climb cutting conditions, such as mentioned, occur when thework-contacting side of a cutter such as 2H), Fig. 9, is moving in thesame direction as the table 22. The cutter periphery moves much fasterthan the table, and under climb-cutting conditions the cutting pressureis negative, that is to say the cutter urges the table ahead of itstransmission whereby the torque is negative as compared with conditionswhere the cutter opposes table movement. If the table screw such as EUis of so-called quick pitch, that is to say with relatively high threadangle whereby it is not self-locking, such negative cutting pressure andtorque may cause overrun with resulting chatter or damage even wherethere is no axial lost motion between the screw and nut, the negativecutting pressure operating on the screw to cause screw rotation andnegative torque on the drive train, resulting in table movement ahead ofthe transmission to the extent of any rotational lost motion existing inthe table driving train.

Rotational overrun caused by negative cutting pressure and negativetorque may be prevented either by setting up a back pressure orresistance suflicient to balance the negative cutting pressure, wherebyto continuously effect positive torque on the table drive train, or byincreasing the friction pressure between the screw and nut threadssufficiently to make the quick pitch screw self-locking in its action,whereby to prevent overrun and negative torque irrespective of thenegative cutting pressure.

There will first be described means for preventing negative torque bymeans opposing negative cutting pressure.

In the device of Fig. 8 the piston 202 receives pressure fluid from thepump I 55 and torque measuring device 49, whereby to eliminate axialbacklash between the screw 60 and nut 64 substantially as previouslydescribed. In addition there is torque controlled brake means, generallydenoted as 214, for opposing negative cutting pressure to continuouslymaintain a positive torque on the driving train of screw 63, as follows:

An endwise movable wedge member 255 is arranged in a recess in saddle23, the saddle forming a wedge abutment in the one lateral directionthrough anti-friction rolls such as 2I5a. In the other lateral directionthe Wedge thrusts against an angular lateral guide surface 2H5 of table22, preferably through an adjustable table gib 22a of conventional typeand anti-friction rolls such as N51). The wedge ZIE is continuouslyurged in wedging direction, whereby to increase the friction resistanceto table movement in its slideways, by the means of a pivoted lever 2Hand an adjustable spring 2&8. The spring pressure is opposed by a pistondevice H9 deriving fluid pres.- sure from pump Hi5.

One or more of the brake devices such as 2% may be used, suflicient toeffect table resistance,

when the springs such as ZIB are not opposed, to prevent forward tablemovement under the conditions of maximum negative cutting pressure. Thepiston devices such as 2P3 are so proportioned that the torquecontrolled fluid pressure will reduce the table friction set up by thewedges such as 2I5 substantially to zero at the point where positivecutting pressure, during normal cutting, is substantially of the samevalue as the maximum negative cutting pressure just mentioned. Undersuch conditions the load on the table transmission will always bepositive and will vary in a characteristic manner charted in Fig. 8A.The increase in the positive torque through torque measuring device 9operates to increasingly oppose the spring 2H! and reduce the wedgepressure, but sufiicient resistance to tabl movement will be maintainedto prevent overrun under any cutting conditions.

The mode of operation characterized by the chart Fig. 8A is somewhatwasteful of power, since considerable frictional resistance is operating during positive cutting pressures, when it is not needed,particularly if the axial lost motion of the screw is eliminated asstated. To avoid such lost power the brake friction may be controlled tobe operative only when the cutting conditions effect negative cuttingpressures.

Referring to Figs. 1, 9, the spindle 2I may be operated either in theforward or reverse directions indicated in Fig. 9, according to thepositioning of the spindle reverser lever 220, Figs. 1, 8. The table 22may be operated in either the forward or reverse directions indicatedaccord ing to the positioning of the lever I51, Figs. 2, 8. As has beenstated, the cutter 2m can only operate to urge the table ahead of itstransmission, whereby to effect negative cutting pressure, when theperiphery of the cutter at the point where it engages the work is movingin the same direction as the table. Such negative cutting pressurecondition will occur only during the combinations, Fig. 9, of spindleforward, table reverse and of spindle reverse, table forward. During thespindle forward, table forward and during spindle reverse, table reversecombinations the cutting pressure will be positive.

The control levers 220 and I51, just mentioned are respectivelyconnected for operation of control valves MI, 222, Figs. 8, 10, seriallyarranged in the pressure line I08 between the pump I05 and torquemeasuring device 49, the valves being positioned beyond the point oftake-off of the branch lines leading to piston 2I9 and to the overloaddevice I98. The control connections may be of any suitable type andtherefore are diagrammatically indicated, as at 220a, I5Ia. Each of thevalves 22I, 222 have valve passageways at different levels, such as thepassageways 22m, 22m, Fig. 10, for the valve 22I controlled from spindlereverse lever 220, and passageways 222a, 2221) for the valve 222controlled from the table reverse lever I 51. The connections 229a,I5'Ia, Fig. 8, are such that in each instance the movement of theassociated reverser lever during reversal rotates the connected valvedegrees, and the valves are provided with ports and passageways, asshown in Fig. 10, such that in the spindle forward, Fig. 9, position ofthe spindle reverse lever 220, and the table forward, Fig. 9, positionof the table reverse lever I57, the passage I98 is closed by the valvesagainst flow of fluid to the torque measuring device 49. Under suchcondition the maximum pressure of pump I05, as determined by the reliefvalve I98, will operate on the piston 259 and the spring 2I8 will becompletely overcome, whereby to entirely relieve the table 22 of anyfriction set up by the wedge device 2I5. The arrangement of the portsand passageways also blocks th channel I08, as will be apparent, Fig.10, when the valves are each turned 90 de- 1 example, by'a hand crank(not shown) applied to thesquared end 60a of-table screw 60,:and 'tablemanual movement will therefore not be :grees for the spindlereverseyandtable reverse combination, Fig. 9.

However, if only one of the=valves 22l, 222, Fig. 10, is turned 90degrees from' the position shown in Fig. 10, whereby to effect eitherthe spindle forward, table reversecombination or the spindle reverse,table forward combination, Fig. 9, fluid will pass the valves to thetorque measuring device 49, which then will control the piston M9 toregulate the table brake 2R4 aspreviously described.

The specific form of the connections l5'la and 220a diagrammaticallyshown in Figs. 8, 11 will be determined by the nature of the controlmovements of the corresponding operation, which in this instance are thehand levers I51 and 220.

Thus, the said copending application Serial 330,051, of which this caseis a division, is in turn a division and continuation of the copendingapplication Serial No. 162,977 now resulted in Patent No. 2,204,693,issued June 18, 1940. Said copending antecedent applications disclosethat the table reverser 54 is in this instance controlled by rotation ofthe hand lever I51 through a predetermined angle about a vertical axis.Any suitable mechanical or other connection [51a which will efl'ect therequired 90 rotation of the valve 222 in the proper directions duringthe rotation of lever l 51 from table forward to reverse positons orvice versa will answer the purposes of the required control of valve222.

Similarly, the spindle reverser lever 220 is, in this instance,rotatable through a predetermined angle about the horizontal axis of itssupporting shaft for effecting forward or reverse spindle rotation, asby the adjustment of a suitable spindle reverser clutch such, forexample, as is shown in the Patent No. 2,203,743, issued June 11, 1940.Any suitable mechanical or other connection 220a which will eifect the90 rotation of valve 22l in the proper directions during the rotation oflever 220 from forward to reverse spindle drive positions and vice versawill answer the purposes of the required control of valve 22L With thevalves 22l, 222 controlled as described, there will be no back pressureset up by the wedge device 2l5 during positive cutting pressure, and thecharacteristic chart for cutting pressure and torque will then'be asshown in Fig. 8A. This provides table back pressure sufficient tomaintain a positive torque preventing overrun during any negativecutting pressure conditons, but without material back pressure whichwould cause waste of power during positive cutting pressure conditions.

The torque controlled backlash eliminating deviceof Fig. 8, operatedfrom piston 202, Figs. 3, 7, ,8, operates to avoid possibility of axiallost motion. However, as shown in Fig. 8, the piston 202 is connected toreceive pressure fluid only through valves 22l, 222, whereby the fluidpressure on piston 202 is operative only during negative cuttingpressure conditions. A preferred constant pressure may be applied to beoperable at other times as, for example, by a spring 225, Fig. 8.

It will benoted that the valve 222, Figs. 8, 10, operates to close thechannel I08, whereby to release the brake pressure opposing tablemovement, as described, whenever the table reverser lever is in centralposition, as willbe apparent in Fig. 10. This is the position ofthe'lever when- "cverthe table is to be:manuallyoperatednas, for

. rates, as hasbeen stated, and to close the channel I00, Fig. 8,whereby to eliminate the brake during quick traverse rate movements,there is provided a valve 220, Figs. 8, 10, connected for operation fromlever I51 as by connecting means I513), to shift the valve to the openposition shown in Fig- 10 in the feed rateposition of lever I51, and torotate thevalve to closed position when lever I5! is positioned forquick traverse rate.

Similarly to the control of valves22l, 222 from the levers I51 and .220,any suitable connection l5?!) may be used for the control of valve 226from lever I51. In the present instance the lever ISTeffectsalternativefeed or quick traverse table movements bymovements about ahorizontal'axis for the shiftin ofthe clutch 39, as is fully explainedin said antecedent application Serial No. 162,977 now resulted in PatentNo. 2,204,693, issued June 18, 1940. Any suitable mechanical or other.connection l5lb may be used which will shift the valve 226 from open toclosed position or vice versa, as described, in accordance with themovements of lever I51 to feed or to quick traverse position about itshorizontal axis.

There will next be described a device for preventing negative torque bymeans increasing the iriction between the screw and nut threadssufficiently to make quick pitch screws self-locking in operation, aspreviously mentioned.

In the device of Fig. 11 the screw 60 is provided with torque controlledbacklash eliminating means cooperative with the fixed nut 64 andincluding a piston device 20!, similarly to generally denoted bythe'numeral 230.

.The pressure means 230, Fig. 11, includes an axially slidable, nut 23lwhich is prevented from rotation by'a key such as 23l a. A pivoted lever232; provides spaced fork portions for passage of screw 60 therebetween,and nut abutment .pressure being opposable by a piston 234.

The threads. of 1 nuts 64 and 23l .are respectively pressed against. theoppositefaces'of the threads of screw 00 by. the action of spring 233',

the engaged'surfaces acting as a brake resisting rotation of .screw' 00.At, the relatively low wrotational speds of, screw 00 during feed ratemotion of the table the braking efiect varies .sub-

, stantiallyin accordance with the spring pressure. Spring 233-may beso; proportioned that,

when unopposed; thebraking effect is sufficient to prevent the maximumavailable negative cutting pressure fromv causing rotational overrun ofthe screw, whereby to prevent overrun caused by rotational lost motionin-ithe screw driving train. Since the. screw will ordinarily .benearlyself-locking without. the brake,.the

brakepressure and; power requiredLtoprevent means of valves 22], 222,226 in the manner explained for the brake piston 2l9 of the device ofFig. 8, whereby to eliminate the brake action during positive cuttingpressure conditions, dur- .ing hand feed operations and during quicktraverse rate movements. A characteristic cutting pressure and torquechart for this mode of operation of the device of Fig. 11 is shown inFig. 11A.

The device of Fig. 11 may also be operated in such manner as to preventoverrun by a combination of the methods previously mentioned, that is tosay in part by opposing the negative cutting pressure and in part by thescrew-brake action effecting self-locking operation of the screw. Forsuch mode of operation the spring 233 is proportioned for the unopposedspring to provide pressure materially in excess of that required for themode of operation previously described, and the torque controlled pistondevice 234 is so proportioned as to substantially completely relieve thenut 23! from the spring pressure at the point where the positive cuttingpressure is equal in numerical value to the maximum negative cuttingpressure. In such case, and with the valves controlled from the leversI51, 220 as described, there will result a force diagram similar to thatof Fig. 8B, but the combination of direct nut pressure and screw-brakeeffect will modify the force diagram somewhat as indicated in Fig. 11B.

The mode of operation of the device of Fig. 11 may be further modifiedfor the spring 233, etc., to operate as a backlash eliminating device.For this result spring 233 is so proportioned that when unopposed itmaintains the nut 23! to the limit of its possible right-hand movement,Fig. 11, that is to say with the screw 60 forced against the fixed nut64, under conditions of maximum negative cutting pressure tending toforce the screw to the left, Fig. 11, and the torque controlled piston234 is so proportioned as to substantially completely relieve nut 23!from spring pressure at the point where the positive cutting pressure isequal in numerical value to the maximum negative cutting pressure. Insuch case the threads of screw 60 will be continuously maintained inpressure contact with the same side faces of the threads of nut 64 andany axial lost motion, as well as rotational overrun will be eliminated,whereby the piston devic 202 will be unnecessary for the purpose. Thecharacteristic force diagram will then be substantially as in Fig. 8B.

It will be noted that, as to the last described modifications of themode of operation of the structure of Fig. 11, the device will operateas described only for one direction of negative cutting pressure, sincethe spring 233 and piston operated from spindle reverser lever 220.Since the necessary structure for such control will be obvious, it isnot shown.

What is claimed is:

1. In a machine tool having a table and a reversibly rotatable spindle,the combination of spindle transmission and control means including ashiftable reverser member, a table transmission including a torqueresponsive device, adjustable mechanism for controlling a force urgingsaid table ahead of its transmission, an automatic adjusting connectionfor adjustment of said mechanism in accordance with the torque responseof said device, and control means for said mechanism connected foroperation at least in part in accordance with the position of saidspindle reverser member.

2. In a machine tool having a reversibly operable table and a reversiblyrotatable spindle, the combination of table transmission and controlmeans including a shiftable table reverser member, spindle transmissionand control means including a shiftable spindle reverser member,mechanism for controlling a force urging said table ahead of itstransmission, and control means for said mechanism connected foroperation in part in accordance with the position of said table reversermember and in part in accordance with the position of said spindlereverser member.

3. In a machine tool having a reversibly operable table and a reversiblyrotatable spindle, the combination of table transmission and controlmeans including a torque responsive device and a shiftable tablereverser member, spindle transmission and control means including ashiftable spindle reverser member, adjustable mechanism for controllinga force urging said table ahead of its transmission, an automaticadjusting connection for adjusting said mechanism in accordance with thetorque response of said device, and control means for said mechanismconnected for operation in part in accordance with the position of saidspindle reverser member and in part in accordance with the position ofsaid table reverser member.

4. In a machine tool having a reversibly operable table, the combinationof a table transmission and control means including a torque responsivedevice and a shiftable table reverser member, adjustable mechanism forcontrolling a force urging said table ahead of its transmission, anautomatic adjusting connection for adjusting said mechanism inaccordance with the torque response of said device, and control meansfor said mechanism connected for operation at least in part inaccordance with the position of said table reverser member.

5. In a machine tool having a reversibly operable table, the combinationof table transmission and control means including a torque responsivedevice and a member shiftable for alternative feed or quick traverserates and a shiftable reverser member, adjustable mecha nism forcontrolling a force urging said table ahead of its transmission, anautomatic adjusting connection for adjusting said mechanism inaccordance wtih the torque response of said device, and control meansfor said mechanism connected for operation in part in accordance withthe position of said feed or quick traverse member and in part inaccordance with the position of said table reverser member.

6. In a machine tool having a reversibly operable table and a reversiblyrotatable spindle,

the combination of spindle transmission and control means including ashiftable reverser member, a table transmission and control meansincluding a torque responsive device and a member shiftable foralternative feed or quick traverse rates and a shiftable table reversermember, adjustable mechanism for controlling a force urging said tableahead of its transmission, an automatic adjusting connection foradjusting said mechanism in accordance with the torque response of saiddevice, and control means for said mechanism connected for operation inpart in accordance with the position of said spindle reverser member andin part in accordance with the operation of said table reverser memberand in part in accordance with said shiitable feed or quick traversemember.

7. In a machine tool having a table, the combination of a table trainincluding a torque responsive device, brake means opposing said trainincluding a pressure means urging said brake means in braking direction,adjustable mechanism for opposing said pressure means, and an automaticadjusting connection for adjusting said mechanism in accordance with thetorque response of said device.

8. A machine tool comprising ab-ase, an operating member movably mountedon said base, a rotary power operated driving train selectivelyconnectible to actuate said operating member, a variable resistancedevice disposed to oppose movement of said operating member in manner toprevent overrunning thereof, and means responsive to torque exerted bysaid rotary driving train to vary the opposition of said resistancedevice, whereby the resistance to movement of said operating member maybe adjusted inversely to the driving torque.

9. In a power transmission mechanism for driving a movable element of amachine tool, a rotary power driven member operatively connected toefiect movement of said machine tool element, resistance meansoperatively connected to oppose movement of said element for preventingovertravel thereof relative to said power driven member, and meansresponsive to torque exerted by said power driven member to regulatesaid resistance means, whereby the resistance exerted in opposition tomovement of said element may be adjusted in accordance with the drivingtorque exerted to effect movement of said element.

10. In a machine tool, a supportingframe, a member movably mounted onsaid frame, power operated rotary driving means selectively operable tomove said member, adjustable movement resisting means selectivelyoperable to oppose movement of said member in manner to preventoverrunning thereof, torque responsive means associated with saiddriving means in manner to function in response to torque being transmitted thereby, and control means operating in response to said torqueresponsive means and functioning to adjust said movement resistingmeans, whereby said resisting means may be adjusted in manner to reducethe resistance in accordance with increase in the driving torque.

FRED A. PARSONS.

